It is known to separate the solid component of slurries or sewage from the liquid by means of filtering cases, with a filter cloth across their walls, wherein the solid is separated from the liquid by gravity. A case of this kind is disclosed, for example, in Italian patent application 21480-B/84.
Dehydration by gravity filtration, which takes place along with natural evaporation of the water contained in a slurry being processed, requires, however, a fairly long time. As an example, in cold damp weather, processing time and/or the attainable results may be unsatisfactory.
To shorten the dehydration time, it has been thought of subjecting a slurry being processed to a pressure, by superimposing a number of cases on one another.
However, that approach has shown to be hardly practicable or even wholly unpracticable because the pressure on the slurry, due to the weight of the stacked cases, reduces itself at most to few marginal areas, to merely produce, if any, a slightly increased initial dehydration, or to concentrate over a central area of the cases, placed the one within another, producing slurry leakage past the case peripheral rims.
Dehydration time has been successfully reduced by stacking together filtering cases having flexible walls, such as filter bags.
In this instance, the effect of stacked bags is that an improved distribution of pressure is brought about, and hence, a higher rate of slurry dehydration without causing it to leak out or drop out.
Flexible wall cases require, however, some auxiliary means of supporting them in the stacked arrangement, and are more difficult to manipulate and handle.
The problem underlying the present invention is to provide a filter case of the rigid type which affords a faster rate of dehydration of civil and industrial slurries, while obviating all the drawbacks which affect the cited prior art.